Electronic article surveillance (EAS) systems are generally known in the art for the prevention or deterrence of unauthorized removal of articles from a controlled area. In a typical EAS system, EAS markers (known as tags or labels) are designed to interact with an electromagnetic field located at the exits of the controlled area, such as a retail store. These EAS markers are attached to the articles to be protected. If an EAS tag is brought into the electromagnetic field or “interrogation zone,” the presence of the tag is detected and appropriate action is taken, such as generating an alarm. For authorized removal of the article, the EAS tag can be deactivated, removed or passed around the electromagnetic field to prevent detection by the EAS system.
EAS systems typically employ either reusable EAS tags or disposable EAS tags or labels to monitor articles to prevent shoplifting and unauthorized removal of articles from the store. The reusable EAS tags are normally removed from the articles before the customer exits the store. The disposable tags or labels are generally attached to the packaging by adhesive or are located inside the packaging. These tags typically remain with the articles and must be deactivated before they are removed from the store by the customer. Deactivation devices may use coils which are energized to generate a magnetic field of sufficient magnitude to render the EAS tag inactive. The deactivated tags are no longer responsive to the incident energy of the EAS system so that an alarm is not triggered.
Radio-frequency identification (RFID) systems are also generally known in the art and may be used for a number of applications, such as managing inventory, electronic access control, security systems, and automatic identification of cars on toll roads. An RFID system typically includes an RFID reader and an RFID device. The RFID reader may transmit a radio-frequency carrier signal to the RFID device. The RFID device may respond to the carrier signal with a data signal encoded with information stored by the RFID device.
The market need for combining EAS and RFID functions in the retail environment is rapidly emerging. Many retail stores that now have EAS for shoplifting protection rely on bar code information for inventory control. RFID offers faster and more detailed inventory control over the bar code. Retail stores already pay a considerable amount for hard tags that are re-useable. Adding RFID technology to EAS hard tags could easily pay for the added cost due to improved productivity in inventory control as well as loss prevention.
There have been attempts to incorporate both EAS and RFID capabilities within one security tag, but these attempts have been met with difficulties. One manner in which a combination EAS/RFID label (or tag) may be utilized is to put the EAS-related components together with the RFID-related components and package them together in a single housing. However, electrical or electro-mechanical interacting factors may affect the performance of either the EAS function and/or the RFID function. Placing the RFID label on top of the EAS label is the most convenient way to incorporate both components in a single housing since this saves space, but this may result in substantial de-tuning and signal loss of the RFID label. For example, in a typical RFID device, performance of the RFID label is typically very sensitive to impedance matching of an application specific integrated circuit (“ASIC”)/lead frame assembly for the RFID device to the effective impedance of an RFID antenna mounted on a substrate. Other objects surrounding the RFID label may also contribute to either the effective impedance or the absorption of electromagnetic energy used to read the RFID label.
Some existing 2450 MHz EAS/RFID combination labels have used a configuration where an RFID label and an EAS label are placed in an overlapping configuration. However, this particular configuration tends to lead to considerable degradation in the RFID label detection capabilities. Other configurations place the RFID and EAS components in an end-to-end or slightly overlap arrangement. However, this results in a tag size that is prohibitively large. If the RFID and EAS components are placed in a side-by-side configuration, the result is often an irregular RFID detection pattern. Thus, designs which have been able to successfully market a combination EAS/RFID tag without degrading the performance of the RFID detection pattern are not known. Most applications using combined EAS and RFID detection of tagged items use EAS and RFID labels that are mounted separately. But by mounting the EAS and RFID components separately, the components occupy considerably more space on the tagged item.
Security tags including an EAS component in combination with an RFID component with a hybrid antenna inlay are described in Applicants' co-pending application Ser. No. 11/667,743 filed Nov. 15, 2005, application Ser. No. 11/667,742 filed Nov. 15, 2005, application Ser. No. 11/939,851 filed Nov. 14, 2007, and application Ser. No. 11/939,921 filed Nov. 14, 2007. The disclosures of these applications are herein incorporated by reference.
In the devices disclosed in application Ser. Nos. 11/939,851 and 11/939,921, the RFID component includes a hybrid antenna inlay. The hybrid antenna RFID element at least partially overlaps the EAS element and a small spacer is disposed therebetween, such as a low foam insert. The RFID element read range is affected and controlled by the spacing between the RFID element and the EAS element.
While these prior art arrangements do allow a smaller overall size of the security tag and provide acceptable RFID performance as compared with other devices, it has been discovered that placement of the RFID chip connected to the magnetic loop of the hybrid antenna adjacent to or near the EAS element results in a significant de-tuning of the RFID element.
Therefore, what is needed is a combination EAS and RFID security tag with a housing configured for optimum geometric placement of the RFID and EAS elements for improved near field and far field RFID performance as compared with existing devices.